Description

Large patches of chalk and soft limestone are occasionally covered entirely by Polydora sp. tubes to the exclusion of almost all other species. This tends to occur in highly turbid conditions and spans the infralittoral and circalittoral in limestone areas such as the Great and Little Ormes (North Wales) and Gower (South Wales). It is even present on the lower shore in the Severn estuary. The boring form of the sponge Cliona celata often riddles the surface layer of the stone. Other sponges present include Halichondria panicea, Haliclona oculata and Hymeniacidon perlevis (syn. Hymeniacidon perleve). Polydora sp. also frequently occurs in small patches as part of other biotopes (e.g. FluCoAs). Other species present include Alcyonium digitatum, Sarcodictyon roseum, the hydroids Halecium halecinum, Abietinaria abietina and Tubularia indivisa, the ascidians Clavelina lepadiformis, Botryllus schlosseri and Morchellium argus, the anemones Urticina felina, Metridium dianthus (syn. Metridium senile) and Sagartia elegans and the bryozoans Flustra foliacea and a crisiid turf. The starfish Asterias rubens, the crabs Inachus phalangium and Carcinus maenas, the polychaete Spirobranchus triqueter (syn. Spirobranchus triqueter), the barnacle Balanus crenatus and the brittlestar Ophiothrix fragilis may also be seen. Please note: this biotope may extend into the infralittoral and littoral zone in areas where water turbidity is sufficiently high. (Information taken from Connor et al., 2004).

Depth range

Lower shore, 0-5 m, 5-10 m, 10-20 m

Additional information

-

Listed By

- none -

Further information sources

Habitat review

Ecology

Ecological and functional relationships

In areas of mud, the tubes built by Polydora ciliata can agglomerate and form layers of mud up to an average of 20 cm thick, occasionally to 50cm. These layers can eliminate the original fauna and flora, or at least can be considered as a threat to the ecological balance achieved by some biotopes (Daro & Polk, 1973).

Daro & Polk (1973) state that the formation of layers of Polydora ciliata tend to eliminate original flora and fauna. The species readily overgrows other species with a flat morphology and feeds by scraping its palps about its tubes, which would inhibit the development of settling larvae of other species.

The activities of Polydora plays an important part in the process of temporary sedimentation of muds in some estuaries, harbours or coastal areas (Daro & Polk, 1973).

Polydora ciliata is predated upon by urchins and in Helgoland there is a close relationship between the distribution of Polydora ciliata and Echinus esculentus. Echinus esculentus grazes almost exclusively on the Polydora ciliata carpets and takes its main food not from biodetritus and animals living between the Polydora chimneys but by feeding on the worm itself. To reach the worm, Echinus esculentus has to scrape away between 0.5and 1.2 cm of solid rock and this feeding behaviour is responsible for the bioerosion of rocks in the Helgoland area by an estimated 1cm per annum (Krumbein & Van der Pers, 1974).

Seasonal and longer term change

The early reproductive period of Polydora ciliata often enables the species to be the first to colonize available substrata (Green, 1983). The settling of the first generation in April is followed by the accumulation and active fixing of mud continuously up to a peak during the month of May, when the hard substrata are covered with the thickest layer of mud. The following generations do not produce a heavy settlement due to interspecific competition and heavy mortality of the larvae (Daro & Polk, 1973). Later in the year, the surface layer cannot hold the lower layers of the mud mat in place, they crumble away and are then swept away by water currents. The empty tubes of Polydora may saturate the sea in June. Recolonization of the substratum is made possible, when larva of other species are in the plankton so recolonization by Polydora may not be as successful as earlier in the year.

Habitat structure and complexity

The biotope has very little structural complexity as Polydora tubes aggregate to form layers of muddy tubes on soft rock. Polydora mats tend to be single species providing little space for other fauna or flora. A Polydora mud is about 20cm thick, but can be up to 50cm thick.

Productivity

Productivity in MCR.Pol is mostly secondary, derived from detritus and organic material. Macroalgae are absent from the biotope. The biotope often occurs in nutrient rich areas, for example, close to sewage outfalls. Allochthonous organic material is derived from anthropogenic activity (e.g. sewerage) and natural sources (e.g. plankton, detritus). Autochthonous organic material is formed by benthic microalgae (microphytobenthos e.g. diatoms and euglenoids) and heterotrophic micro-organism production. Organic material is degraded by micro-organisms and the nutrients are recycled. The high surface area of fine particles that covers the Polydora mud provides surface for microflora.

Recruitment processes

The spawning period for Polydora ciliata in northern England is from February until June and three or four generations succeed one another during the spawning period (Gudmundsson, 1985). After a week, the larvae emerge and are believed to have a pelagic life from two to six weeks before settling (Fish & Fish, 1996). Larvae are substratum specific selecting rocks according to their physical properties or sediment depending on substrate particle size.
Larvae of Polydora ciliata have been collected as far as 118km offshore (Murina, 1997). Adults of Polydora ciliata produce a 'mud' resulting from the perforation of soft rock substrates and the larvae of the species settle preferentially on substrates covered with mud (Lagadeuc, 1991).

Time for community to reach maturity

A Polydora biotope is likely to reach maturity very rapidly because Polydora ciliata is a short lived species that reaches maturity within a few months and has three or four spawnings during a breeding season of several months. For example, in colonization experiments in Helgoland (Harms & Anger, 1983) Polydora ciliata settled on panels within one month in the spring. The tubes built by Polydora agglomerate sometimes to form layers of mud up to an average of 20cm thick. However, it may take several years for a Polydora ciliata 'mat' to reach a significant size.

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

Additional information

Sensitivity characteristics of the habitat and relevant characteristic species

CR.MCR.SfR.Pol is a sublittoral biotope occurring in moderately exposed areas with strong, but also moderately strong and weak tidal streams (Connor et al., 2004). This biotope is defined by occurring in soft rock, such as chalk and soft limestone, in areas where water turbidity is high. Large patches of chalk and soft limestone are occasionally covered entirely by Polydora sp. tubes to the exclusion of almost all other species (Daro & Polk, 1973). The species readily overgrows other species with a flat morphology and feeds by scraping its palps about its tubes, which would inhibit the development of settling larvae of other species. For this reason, the mat of Polydora spp. tubes is considered as the defining characteristic of this biotope. In the north west of Europe, Polydora ciliata has been mainly associated to limestone rock and stones (Hayward & Ryland, 1995b), so it is likely that this species is characteristic of this this biotope and is therefore the focus of this assessment as an example of tube building Polydora spp. In this biotope Polydora spp. (and their tubes) are therefore the key structuring and defining element. A range of other epifaunal species are present in patches including sponges, hydroids, barnacles, ascidians and anemones. These contribute to species richness and diversity but are not considered key characterizing, defining or structuring species and are not considered within the assessments. More information on these species can be found in other biotope assessments available on this website.

The soft rock substratum is considered a key element defining the habitat and supporting the development of this biotope. The substratum is therefore considered in sensitivity assessments where the pressure may alter or change it.

Resilience and recovery rates of habitat

Polyodra is a small, sedentary, burrowing polychaete worm up to 3 cm long. All Polydora spp. make a U-shaped tube from small particles (Hayward & Ryland, 1995b). Polydora ciliata usually burrows into substrata containing calcium carbonate such as limestone, chalk and clay, as well as shells or oysters, mussels and periwinkles (Fish & Fish, 1996). The sexes are separate and breeding has been recorded in spring in a number of locations. In northern England, spawning has been recorded to occur from February until June and three or four generations succeed one another during the spawning period (Gudmundsson, 1985). Eggs are laid in a string of capsules that are attached by two threads to the wall of the burrow (Fish & Fish, 1996). After a week the larvae emerge and are believed to have a pelagic life of from 2-6 weeks before settling. Length of life is no more than 1 year (Fish & Fish, 1996). Larvae of Polydora ciliata have been collected as far as 118 km offshore (Murina, 1997). Larvae settle on specific substratum types, selecting rocks according to their physical properties or sediment depending on substrate particle size. Adults of Polydora ciliata produce a 'mud' resulting from the perforation of soft rock substrates and the larvae of the species settle preferentially on substrates covered with mud (Lagadeuc, 1991). The tubes built by Polydora agglomerate sometimes to form layers of mud up to an average of 20 cm thick. However, it may take several years for a Polydora ciliata 'mat' to reach a significant size (Hill, 2007). However, interspecific competition and heavy mortality of the larvae have been observed on Polydora mats (Daro & Polk, 1973).

The early reproductive period of Polydora ciliata often enables the species to be the first to colonize available substrata (Green, 1983). The settling of the first generation in April is followed by the accumulation and active fixing of mud continuously up to a peak during the month of May. The following generations do not produce a heavy settlement due to interspecific competition and heavy mortality of the larvae (Daro & Polk, 1973). Later in the year, the surface layer cannot hold the lower layers of the mud mat in place, they crumble away and are then swept away by water currents. The empty tubes of Polydora may saturate the sea in June. Recolonization of the habitat later in the year may be inhibited by other species that colonize and compete for rock and therefore later settlements may not result in the formation of this biotope.

A Polydora biotope is likely to reach maturity very rapidly because Polydora ciliata is a short lived species that reaches maturity within a few months and has three or four spawnings during a breeding season of several months. For example, in colonization experiments in Helgoland (Harms & Anger, 1983) Polydora ciliata settled on panels within one month in the spring.

Resilience assessment: Removal of the characterizing species Polydora would likely result in the biotope being lost and re-classified. Polydora is short lived species, reaching maturity within a few months, and communities appear to be annual, sustained by three or even four generations succeeding one another and resulting in planktonic larvae that can be found throughout the year (Daro & Polk, 1973). In the event of a large portion of the Polydora community being lost, the biotope is likely to reach maturity very. For as long as the substrate nature of the biotope remains suitable for the settlement of Polydora recruits, the biotope is likely to recover fully within two years, hence resilience has been assessed as High.

NB: The resilience and the ability to recover from human induced pressures is a combination of the environmental conditions of the site, the frequency (repeated disturbances versus a one off event) and the intensity of the disturbance. Recovery of impacted populations will always be mediated by stochastic events and processes acting over different scales including, but not limited to, local habitat conditions, further impacts and processes such as larval-supply and recruitment between populations. Full recovery is defined as the return to the state of the habitat that existed prior to impact. This does not necessarily mean that every component species has returned to its prior condition, abundance or extent but that the relevant functional components are present and the habitat is structurally and functionally recognizable as the initial habitat of interest. It should be noted that the recovery rates are only indicative of the recovery potential.

Hydrological Pressures

Murina (1997) categorized Polydora ciliata as a eurythermal species because of its ability to spawn in temperatures ranging from 10.6-19.9°C. This is consistent with a wide distribution in north-west Europe which extends into the warmer waters of Portugal and Italy (Pardal et al., 1993; Sordino et al., 1989). In the western Baltic Sea, Gulliksen (1977) recorded high abundances of Polydora ciliata in temperatures of 7.5 to 11.5°C and in Whitstable in Kent, where sea temperatures varied between 0.5 and 17°C (Dorsett, 1961). Growth rates may increase if temperature rises. For example, at Whitstable in Kent, Dorsett (1961) found that a rapid increase in growth of Polydora ciliata coincided with the rising temperature of the seawater during March.

Sensitivity assessment: Typical surface water temperatures around the UK coast vary, seasonally from 4-19°C (Huthnance, 2010). No information was found on the maximum temperature tolerated by Polydora ciliata. However, it is likely that the species is able to resist a long term increase in temperature of 2°C and may resist a short term increase of 5°C. Resistance and resilience are therefore assessed as High and the biotope is judged as Not Sensitive.

Murina (1997) categorized Polydora ciliata as a eurythermal species because of its ability to spawn in temperatures ranging from 10.6-19.9°C. This is consistent with a wide distribution in north-west Europe. In the western Baltic Sea, Gulliksen (1977) recorded high abundances of Polydora ciliata in temperatures of 7.5 to 11.5°C and in Whitstable in Kent abundance was high when winter water temperatures dropped to 0.5°C (Dorsett, 1961). During the extremely cold winter of 1962/63 Polydora ciliata was apparently unaffected, when temperature anomalies of between 2.5-5.8°C where observed (Crisp, 1964).

Sensitivity assessment: Typical surface water temperatures around the UK coast vary, seasonally from 4-19°C (Huthnance, 2010). Polydora ciliata is likely to be able to resist a long term decrease in temperature of 2°C and may resist a short term decrease of 5°C. Temperature may act as a spawning cue and an acute or chronic decrease may result in some delay in spawning, however this is not considered to impact the adult population and may be compensated by later spawning events. Resistance and resilience are therefore assessed as High and the biotope judged as Not Sensitive.

Polydora ciliata is a euryhaline species inhabiting fully marine and estuarine habitats. However, there are no records of the species or the biotope occurring in hypersaline waters.

Sensitivity assessment: A long-term increase in salinity at the pressure benchmark level is likely to result in the death of many individuals. Resistance is therefore assessed as Low and resilience is likely to be High so the biotope is considered to have Low sensitivity to an increase in salinity at the pressure benchmark level.

Polydora ciliata is a euryhaline species inhabiting fully marine and estuarine habitats. In an area of the western Baltic Sea, where bottom salinity was between 11.1 and 15.0psu Polydora ciliata was the second most abundant species with over 1000 individuals per m2 (Gulliksen, 1977).

Sensitivity assessment: Records indicate CR.MCR.SfR.Pol occurs in areas of variable (18-35 ppt) salinity (Connor et al., 2004). Polydora ciliata is therefore likely to resist a decrease in salinity at the pressure benchmark level. Resistance is therefore assessed as High and resilience as High (by default) and the biotope is considered Not Sensitive to a decrease in salinity at the pressure benchmark level.

Polydora ciliata colonized test panels in Helgoland in three areas, two exposed to strong tidal currents and one site sheltered from currents (Harms & Anger, 1983). Very strong water flows may sweep away Polydora colonies, where these are present as a thick layer of mud on a hard substratum.

The most damaging effect of increased flow rate (above the pressure benchmark) could be the erosion of the soft rock substratum as this could eventually lead to loss of the habitat.

Sensitivity assessment: CR.MCR.SfR.Pol is recorded in a range of tidal streams, including strong, moderately strong and weak tidal stream conditions (Connor et al., 2004). A change in water flow at the benchmark level of 0.1-0.2 m/s is therefore likely to fall within the normal range of water flows experienced by the biotope. Resistance and resilience are therefore considered to be High and the biotope is assessed as Not Sensitive to a change in water flow rate at the pressure benchmark level.

Changes in emergence are Not Relevant to the biotope, which is restricted to fully subtidal/circalittoral conditions. The pressure benchmark is relevant only to littoral and shallow sublittoral fringe biotopes.

The biotope is found in moderately exposed sites (Connor et al., 2004). Feeding of Polydora ciliata may be impaired in strong wave action and changes in wave exposure may also influence the supply of particulate matter for tube building activities. Decreases in wave exposure may influence the supply of particulate matter because wave action may have an important role in re-suspending the sediment that is required by the species to build its tubes. Food supplies may also be reduced affecting growth and fecundity of the species.

Potentially the most damaging effect of increased wave heights would be the erosion of the soft rock substratum as this could eventually lead to loss of the habitat.

Sensitivity assessment. Some erosion will occur naturally and storm events may be more significant in loss and damage of soft rocks than changes in wave height at the pressure benchmark. The biotope is therefore considered to have High resistance to changes at the pressure benchmark where these do not lead to increased erosion of the substratum. Resilience is therefore assessed as High and the biotope is considered to be Not Sensitive, at the pressure benchmark.

Chemical Pressures

Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

Experimental studies with various species suggest that polychaete worms are quite resistant to heavy metals (Bryan, 1984). Polydora ciliata occurs in an area of the southern North Sea polluted by heavy metals but was absent from sediments with very high heavy metal levels (Diaz-Castaneda et al., 1989).

Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

In analysis of kelp holdfast fauna following the Sea Empress oil spill in Milford Haven the fauna present, including Polydora ciliata, showed a strong negative correlation between numbers of species and distance from the spill (SEEEC, 1998). After the extensive oil spill in West Falmouth, Massachusetts, Grassle & Grassle (1974) followed the settlement of polychaetes in the disturbed area. Species with the most opportunistic life histories, including Polydora ligni, were able to settle in the area. This species has some brood protection which enables larvae to settle almost immediately in the nearby area (Reish, 1979).

Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

Polydora ciliata was abundant at polluted sites close to acidified, halogenated effluent discharge from a bromide-extraction plant in Amlwch, Anglesey (Hoare & Hiscock, 1974). Spionid polychaetes were found by McLusky (1982) to be relatively resistant of distilling and petrochemical industrial waste in Scotland.

Polydora ciliata is frequently found at localities with oxygen deficiency (Pearson & Rosenberg, 1978). For example, in polluted waters in Los Angeles and Long Beach harbours Polydora ciliata was present in the oxygen range 0.0-3.9 mg/l and the species was abundant in hypoxic fjord habitats (Rosenberg, 1977). Furthermore, in a study investigating a polychaete community in the north west Black Sea, Polydora ciliata was observed in all four study sites, including those severely affected by eutrophication and hypoxia as a result of discharges of wastewaters (Vorobyova et al., 2008). However, Polydora ciliata is unlikely to be able to resist anoxic conditions. Hansen et al. (2002) reported near total extinction of all metazoan in the Mariager Fjord (Denmark), including Polydora spp. after a severe hypoxia event that resulted in complete anoxia in the water column for two weeks. Additionally, Como & Magni (2009) investigated seasonal variations in benthic communities known to be affected by episodic events of hypoxia. The authors observed that abundance of Polydora ciliata varied seasonally, decreasing during the summer months, and suggested it could be explained by the occurrence of hypoxic/anoxic conditions and sulphidic sediments during the summer. No details of the levels of dissolved oxygen leading to these community responses were provided.

Sensitivity assessment:Polydora ciliata is frequently found at localities with oxygen deficiency (Pearson & Rosenberg, 1978) and seems to only be affected by severe de-oxygenation episodes. Resistance to de-oxygenation at the pressure benchmark level is likely to be High. Opportunistic Polydora spp. have also repeatedly been reported amongst the first to recover hypoxia events (Hansen et al., 2002; Van Colen et al., 2010) so resilience is likely to also be High. The biotope is therefore considered Not Sensitive to exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for 1 week.

Polydora ciliata is often found in environments subject to high levels of nutrient input. For example, the species was abundant in areas of the Firth of Forth exposed to high levels of sewage pollution (Smyth, 1968), in nutrient rich sediments in the Mondego estuary, Portugal (Pardal et al., 1993) and the coastal lagoon Lago Fusaro in Naples (Sordino et al., 1989). The extensive growths of Polydora ciliata in mat formations were recorded at West Ganton, in the Firth of Forth, prior to the introduction of the Sewage Scheme (Read et al., 1983). The abundance of the species was probably associated with their ability to use the increased availability of nutrients as a food source and silt for tube building.

Sensitivity assessment: The characterizing species of this biotope is likely to be able to resist nutrient enrichment. The biotope is considered Not Sensitive at the pressure benchmark that assumes compliance with good status as defined by the WFD.

In colonization experiments in an organically polluted fjord receiving effluent discharge from Oslo, Polydora ciliata had settled in large numbers within the first month (Green, 1983; Pardal et al., 1993). However, Callier et al. (2007) investigated the spatial distribution of macrobenthos under a suspended mussel culture, in eastern Canada, where the sedimentation of organic matter to the bottom was approx. 1-3 gC/m2/d. Polydora ciliata was recorded as absent in the sites under the suspended mussel farm after one year and as dominant in reference areas of the study. It should be noted that the organic matter input from the mussel farm exceeds the pressure benchmark.

Como & Magni (2009) investigated seasonal variations in benthic communities known to be affected by episodic events of sediment over-enrichment. The authors observed that abundance of Polydora ciliata varied seasonally, and suggested this could be a result of major accumulation of organic C-bounding fine sediments in the study site.

Borja et al. (2000) and Gittenberger & van Loon (2011) in the development of an AMBI index to assess disturbance (including organic enrichment) both assigned Polydora ciliata to their Ecological Group IV ‘Second-order opportunistic species present in slight to pronounced unbalanced situations’.

Sensitivity assessment: The evidence presented suggests Polydora ciliata may not be able to resist organic enrichment that exceeds the pressure benchmark level (Callier et al., 2007) but may not be affected by at the benchmark level. Resistance and resilience are therefore assessed as High and the biotope is considered Not Sensitive to organic enrichment (deposit of 100 gC/m2/yr).

Physical Pressures

All marine habitats and benthic species are considered to have a resistance of None to this pressure and to be unable to recover from a permanent loss of habitat (Resilience is Very Low). Sensitivity within the direct spatial footprint of this pressure is therefore High. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

CR.MCR.SfR.Pol is characterized by the soft rock substratum which supports populations of Polydora sp. tubes. A change to a sedimentary, hard rock or artificial substratum would result in the loss of Polydora, significantly altering the character of the biotope. The biotope would be lost and/or re-classified.

Sensitivity assessment: Resistance to the pressure is considered None, and resilience Very Low based on the loss of suitable substratum to support the community of the characterizing species of Polydora. Sensitivity has been assessed as High. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Removal of the substratum to 30 cm would result in the loss of Polydora sp. tubes. Resistance to the pressure is considered None, and resilience Very Low based on the loss of suitable substratum to support the community of the characterizing species of Polydora. Sensitivity has been assessed as High. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

This biotope is characterized by epifauna occurring on hard rock substratum. The tubes of Polydora spp. are likely to be removed by abrasion as these project above the surface and are not physically robust. Other epifauna associated with this biotope are also likely to be damaged and/or removed by surface abrasion. Some species such as anemones and sponges may be able to rapidly repair damage while others may recolonize rapidly, e.g. barnacles.

Sensitivity assessment. The characterizing Polydora community in this biotope, is considered likely to be damaged and removed by abrasion. As a soft bodied species, Polydora ciliata is likely to be crushed and killed by an abrasive force or physical blow. Erect epifauna are directly exposed to this pressure which would displace, damage and remove individuals. Resistance to abrasion is considered None. However, Polydora is likely to be able to re-establish the lost community rapidly, so resilience of the biotope is assessed as High with the biotope considered to have Medium sensitivity to abrasion or disturbance of the surface of the seabed. The substratum is unable to recover from damage and therefore the biotope would be considered highly sensitivity to abrasion that damaged or removed the soft rock substratum.

Activities that disturb the surface of the mat and penetrate below the surface would remove a significant proportion of the Polydora tubes within the direct area of impact. Biotope resistance is therefore assessed as None and recovery is assessed as High based on the assumption that the suitable substratum to support the community of the characterizing species of Polydora would only be damaged, not lost. Sensitivity is therefore assessed as Medium. The substratum is unable to recover from damage and therefore the biotope would be considered highly sensitivity to physical disturbance that damaged or removed the soft rock substratum. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

CR.MCR.SfR.Pol tends to occur in highly turbid areas (Connor et al., 2004). In the Firth of Forth, Polydora ciliata formed extensive mats in areas that had an average of 68 mg/l suspended solids and a maximum of approximately 680 mg/l, indicating the species is able to tolerate different levels of suspended solids (Read et al., 1982; Read et al., 1983). Occasionally, in certain places siltation is speeded up when Polydora ciliata is present because the species actually produces a 'mud' as it perforates soft rock and chalk habitats and larvae settle preferentially on substrates covered with mud (Lagadeuc, 1991).

Suspended sediment and siltation of particles is important for tube building in Polydora ciliata so a decrease in suspended solids may reduce tube building or the thickness of the mud surrounding the 'colonies'. Daro & Polk (1973) reported that the success of Polydora is directly related to the quantities of muds of any origin carried along by rivers or coastal currents.

An increase in turbidity, reducing light availability may reduce primary production by phytoplankton in the water column. A reduction in primary production in the water column may result indirectly in reduced food supply to the detritus feeding Polydora which in turn may affect growth rates and fecundity.

Sensitivity assessment: An increase in suspended solids at the pressure benchmark level is unlikely to affect the characterizing species of this biotope. However, a decrease in suspended matter in the biotope could result in limitation of material for tube building activity of Polydora and also in the substrate no longer being suitable for colonization by new recruits. Resistance of the biotope is therefore considered to be Low (loss of 25-75%) and resilience is High (following a return to normal conditions) so the biotope is considered to have Low sensitivity to a decrease in suspended solids at the pressure benchmark level.

Adults of Polydora ciliata produce a 'mud' resulting from the perforation of soft rock substrates (Lagadeuc, 1991). A Polydora mud can be up to 50 cm thick, but the animals themselves occupy only the first few centimetres. They either elongate their tubes to reach the surface, or leave them to rebuild close to the surface.

Munari & Mistri (2014) investigated the spatio-temporal variation pattern of a benthic community following deposition of dredged material, at a maximum thickness of 30–40 cm. Polydora ciliata was amongst the first colonizers of the newly deposited sediments. The authors suggested that it was possible that the individuals migrated vertically through the deep layer of dredged sand. This was based on the results of Roberts et al. (1998) who suggested 15 cm as the maximum depth of overburden through which benthic infauna can successfully migrate. After one year, no adverse impact of sand disposal on the benthic fauna was detected on the study site.

Sensitivity assessment: Based on the evidence presented by Munari & Mistri (2014), Polydora ciliata is considered likely to resist smothering by 5 cm of sediment. Resistance and resilience are therefore assessed as High and the biotope is considered Not Sensitive to a ‘light’ deposition of up to 5 cm of fine material in a single discrete event.

Adults of Polydora ciliata produce a 'mud' resulting from the perforation of soft rock substrates (Lagadeuc, 1991). A Polydora mud can be up to 50 cm thick, but the animals themselves occupy only the first few centimetres. They either elongate their tubes, or leave them to rebuild close to the surface.

Munari & Mistri (2014) investigated the spatio-temporal variation pattern of a benthic community following deposition of dredged material, at a maximum thickness of 30–40 cm. Polydora ciliata was amongst the first colonizers of the newly deposited sediments. The authors suggested that it was possible that the individuals migrated vertically through the deep layer of dredged sand. This was based on the results of Roberts et al. (1998) who suggested 15 cm as the maximum depth of overburden through which benthic infauna can successfully migrate. After one year, no adverse impact of sand disposal on the benthic fauna was detected on the study site.

Sensitivity assessment: Polychaete species have been reported to migrate through depositions of sediment greater that the benchmark (30 cm of fine material added to the seabed in a single discrete event) (Maurer et al., 1982). However, it is not clear whether Polydora ciliata is likely to be able to migrate through a maximum thickness of fine sediment that would compare to that investigated by Munari & Magni (2014) because muds tend to be more cohesive and compacted than sand. Some mortality of the characterizing species is likely to occur. Resistance is therefore assessed as Low and resilience as High and the biotope is considered to have Low sensitivity to a ‘heavy’ deposition of up to 30 cm of fine material in a single discrete event.

Polydora ciliata may respond to vibrations from predators or bait diggers by retracting their palps into their tubes. However, the species is unlikely to be affected by noise pollution and so the biotope is assessed as Not Sensitive.

CR.MCR.SfR.Pol is a circalittoral biotope (Connor et al., 2004) and therefore, not directly dependent on sunlight.

Sensitivity assessment. Although Polydora spp. can perceive light, this pressure is not considered relevant. The biotope is considered to have High resistance and, by default, High resilience and therefore is Not Sensitive to the introduction of light.

Polydora ciliata exhibits shadow responses withdrawing its palps into its burrow, believed to be a defence against predation. However, since the withdrawal of the palps interrupts feeding and possibly respiration the species also shows habituation of the response (Kinne, 1970).

Sensitivity assessment:Polydora is likely to be tolerant of visual disturbance. Resistance and resilience are therefore assessed as High and the biotope judged as Not Sensitive to visual disturbance.

Direct, physical impacts are assessed through the abrasion and penetration of the seabed pressures, while this pressure considers the ecological or biological effects of by-catch. Species in this biotope, including the characterizing species Polydora ciliata, may be damaged or directly removed by static or mobile gears that are targeting other species (see abrasion and penetration pressures). Loss of Polydora species and the mat of tubes would alter the character of the biotope resulting in re-classification. Loss of Polydora spp. and the associated epifauna would alter the physical structure of the habitat and result in the loss of the ecosystem functions such as secondary production performed by these species.

Sensitivity assessment. Removal of the characterizing species would result in the biotope being lost or re-classified. Thus, the biotope is considered to have a resistance of None to this pressure and to have High resilience, resulting in the sensitivity being judged as Medium.

Bryan, G.W., 1984. Pollution due to heavy metals and their compounds. In Marine Ecology: A Comprehensive, Integrated Treatise on Life in the Oceans and Coastal Waters, vol. 5. Ocean Management, part 3, (ed. O. Kinne), pp.1289-1431. New York: John Wiley & Sons.

The information (TEXT ONLY) provided by the Marine Life Information Network (MarLIN) is licensed under a Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales License. Note that images and other media featured on this page are each governed by their own terms and conditions and they may or may not be available for reuse. Permissions beyond the scope of this license are available here. Based on a work at www.marlin.ac.uk